Noji S, Nohno T, Koyama E, Muto K, Ohyama K, Aoki Y, Tamura K, Ohsugi K, Ide H, Taniguchi S
Department of Biochemistry, Okayama University Dental School, Japan.
Nature. 1991 Mar 7;350(6313):83-6. doi: 10.1038/350083a0.
Retinoic acid is a putative morphogen in limb formation in the chick and other vertebrates. In chick limb formation, it is thought that retinoic acid is released from the zone of polarizing activity (ZPA) and the concentration gradient of retinoic acid formed from the posterior to the anterior provides positional cues for digit formation. Implantation of a bead containing retinoic acid at the anterior margin of the limb bud induces a mirror-image symmetrical duplication of the digit pattern similar to that observed when the ZPA is grafted into the anterior margin of the host limb bud. Also, the level of endogenous retinoic acid (25 nM on average) is higher in the posterior one third of the limb bud. We found that when the bead containing either retinoic acid or an analogue but not the ZPA, was implanted in the anterior margin of the chick limb bud, expression of the retinoic acid receptor type-beta gene was induced around the bead within 4 h. These results indicate that exogenous retinoic acid is not identical with the ZPA morphogen. As the anterior tissue exposed to retinoic acid has polarizing activity, we conclude that the primary function of exogenous retinoic acid is to induce polarizing activity in the limb bud.
视黄酸被认为是鸡和其他脊椎动物肢体形成过程中的一种假定形态发生素。在鸡的肢体形成过程中，人们认为视黄酸是从极化活性区（ZPA）释放出来的，从后向前形成的视黄酸浓度梯度为指（趾）的形成提供位置线索。将含有视黄酸的珠子植入肢体芽的前缘会诱导指（趾）模式的镜像对称重复，类似于将ZPA移植到宿主肢体芽前缘时观察到的情况。此外，肢体芽后三分之一处的内源性视黄酸水平（平均25 nM）较高。我们发现，当将含有视黄酸或其类似物而非ZPA的珠子植入鸡肢体芽的前缘时，在4小时内珠子周围会诱导视黄酸β型受体基因的表达。这些结果表明，外源性视黄酸与ZPA形态发生素不同。由于暴露于视黄酸的前部组织具有极化活性，我们得出结论，外源性视黄酸的主要功能是在肢体芽中诱导极化活性。
